MODULATION OF S-1 CONFORMATION AND INHIBITION OF THE SKELETAL
MUSCLE S-1-ATPASE BY CALPONIN OF THE MUSSEL
V.V. Sirenko,1 A.H. Simonyan,1 A.V. Dobrzhanskaya,2 N.S. Shelud’ko,2 Yu.S. Borovikov 1,*
1 Institute of Cytology RAS, St. Petersburg, and
2 A.V. Zhirmunsky Institute of Marine Biology, Far Eastern Branch of the RAS, Vladivostok;
* e-mail: boroviko@mail.cytspb.rssi.ru
A novel 40 kDa protein has been detected in native thin filaments from catch muscles of the mussel Crenomytilus
grayanus. In this study, using skeletal muscle actin and S-1, we investigated the effects of the mussel
40-kDa actin-binding protein on the acto•S-1 ATPase activity. On increasing the 40-kDa actin-binding protein
(CaP-40) concentration, the actin-activated ATPase activity decreased, and was inhibited 80 % at a CaP-40 to
actin ratio of 0.5. Polarized fluorimetry technique and glycerinated muscle fibers were used to study effects of
CaP-40 on the orientation and mobility of fluorescent label 1.5-IAEDANS specifically bound to CyS-707 of
myosin subfragment-1 in the absence of nucleotide, and in the presence of MgADP or MgATP. We have concluded
that CaP-40 binding to actin affects the strong binding of myosin to actin but has no effect on the weak
binding. Thus, the influence of the CaP-40 on the formation of strong actomyosin binding forms A•M and
A•M•ADP manifests itself by a decrease in the relative content of myosin cross-bridges strongly bound with
actin, which probably results in a decrease in the relative content of «switch on» actin monomers in thin filaments.
This suggests that, as calponin CaP-40 selects its target the phase of strong actomyosin binding binding
which preceded by a phase generating power stroke.
Key words: calponin-like protein, conformational change of myosin S-1, fluorescence polarization
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